1. Field of the Invention
The present invention relates to a pneumatic timer utilizing the flow resistance of air passing through a narrow passage to produce timing action of a timing member with which an electric switch mechanism is associated to provide an electric output.
2. Description of the Prior Art
A pneumatic timer is used to determine timing by utilizing the flow resistance of air. It is possible to determine timing for various intervals of time by making said flow resistance variable. Generally, a pneumatic timer comprises a timing mechanism which determines timing on the basis of time characteristics determinable as a function of the flow resistance of air, a solenoid mechanism for driving said timing mechanism, and an output mechanism which provides an electric output in accordance with the timing determined by said timing mechanism. Such pneumatic timer presents the following three technical problems: (1) How to construct and arrange in a compact manner said three mechanisms constituting the pneumatic timer; (2) how to facilitate the assembly of said three mechanisms; and (3) how to improve the accuracy of timing action.
However, conventional pneumatic timer designs have failed to offer a satisfactory solution to these problems. For example, when the three mechanisms, which are independently constructed, are assembled or connected together, the assembling error and the dimensional errors of the components of each mechanism directly influence the timing error. Further, the timing mechanism must act slowly while the output mechanism (switch mechanism) must act quickly. Conventionally, the switch mechanism operates on the principle of the snap action of a microswitch. However, such snap action characteristics differ among different switch mechanisms, presenting a problem concerning reliability. Conventionally, with a view to solving this problem, a fine adjusting screw is attached to said microswitch. The use of a microswitch in operative association with the slow action of said timing mechanism, however, is not desirable.
Further, in a pneumatic timer, since the displacing force of a displaceable member included in the timing mechanism is very small, it is required that control of the contact set of the switch mechanism can be effected with a very small force.
Furthermore, it is desirable that conversion between an ON-delay type timer in which timing action is started upon turning-on of power and an OFF-delay type timer in which timing action is started upon turning-off of power can be made as needed.